1. Field of the Invention
The invention relates to speech processing method and apparatus which can be used for recognition of input speech.
2. Related Background Art
Hitherto, as shown in FIG. 3, in a code book, a quantization range is determined by step S31 for determining a min-max quantization range and a quantum is determined in the quantization range in step S32 for determining a quantum by equally dividing the quantization range. Each of the above steps is processed as follows.
&lt;Step S31 of determining min-max quantization range&gt;
With respect to all of the distributions of the dimension of HMM as a statistic model of speech data that is used for speech recognition, a value obtained by adding or subtracting a value which is a predetermined number of times as large as a standard deviation to/from an average of the distributions is derived for every dimension and the maximum value and the minimum value of the resultant value obtained are set to a quantization range of the relevant dimension.
Specifically speaking, the i-dimensional quantization range [R.sub.min.i, R.sub.max.i ] is obtained as follows. ##EQU1## where, m: distribution number (m=1, 2, . . . , M.sub.i) M.sub.i : the total number of i-dimensional distributions
.mu..sub.m,i : average of the i-dimensional m-th distribution PA1 .sigma..sub.m,i : standard deviation calculated from the divergence of the i-dimensional m-th distribution PA1 .alpha.: coefficient to determine the quantization range
FIG. 4 shows an image diagram of the min-max quantization range determining step.
&lt;Step S32 of determining quantum by equally dividing quantization range&gt;
A quantum is determined for every dimension so as to equally divide the quantization range.
When the i-dimensional quantization range is set to [R.sub.min.i, R.sub.max.i ] and the number of quantization steps is equal to N, a j-th (1.ltoreq.j.ltoreq.N) quantum C.sub.i,j is determined by the following equation (3) in step S3 of determining the quantum by equally dividing the quantization range. ##EQU2##
FIG. 5 shows an image diagram of the step of determining the quantum by equally dividing the quantization range.